[codex] Align explorer with OpenGradient brand

[0xadvait]

Summary

• Refreshes the explorer shell, home page, TEE registry, and core listing pages with OpenGradient brand tokens, typography, panels, and navigation styling.
• Makes dark mode the default while keeping the persistent light/dark toggle available on every page.
• Reorients the homepage around OpenGradient AI execution: hero copy now highlights model inference, x402 settlements, TEE attestations, and AI workflow activity.
• Adds a homepage Trusted AI execution module that embeds the TEE registry story with active TEE counts, execution type, approved PCRs, registry links, and live operator previews.
• Cleans up gas tracker cards and replaces broken gas-history errors with a live recent-block utilization fallback.
• Aligns the home page hero/content grid, expands latest transactions to match the left column, and updates Models Hosted to 4,500+.
• Tightens responsive behavior for narrow mobile headers, verified-contract filters, and desktop TEE registry overflow.

Validation

• yarn lint:eslint (0 errors; existing warnings remain)
• yarn lint:tsc
• tsc -p ./tsconfig.json --noEmit
• Pre-commit lint-staged eslint + TypeScript
• Fresh-browser Playwright checks for dark default, homepage AI/TEE content, TEE registry, and no overflow at 320px, 390px, and desktop widths
• In-app browser DOM check for the updated homepage with no console errors
• Earlier Playwright overflow audit across home, transactions, internal transactions, blocks, top accounts, verified contracts, gas tracker, and TEE registry at 320px, 360px, 390px, and desktop widths